1. Field of the Invention
The present invention relates to a light source using a light emitting diode, an illumination device using the light source as a backlight source, and a liquid crystal display device using the illumination device.
2. Description of the Related Art
Recently, light emitting diodes are applied not only to small and medium sized liquid crystal display devices but also to large sized liquid crystal display devices. The recent liquid crystal display device used for a television, personal computer and the like has a smaller dimension in a direction perpendicular to a display surface of a flat panel display than that of a conventional CRT-based television which emits an electron beam. In order to reduce the dimension, the recent liquid crystal display device uses side light sources, which are located on both sides of a display screen and emit light to a light guide plate. The light emitted by the side light sources is diffusely reflected and directed to a back portion of a liquid crystal section by the light guide plate as a surface light source. On the other hand, a conventional technique uses a light source, which is located on the back side of a screen and emits light to a back portion of a liquid crystal section, which is controlled by applying a voltage between electrodes.
In each of small and medium sized liquid crystal display devices, light emitting diodes are used as the side light source to achieve a thin and lightweight light source module. For large sized liquid crystal display devices, it is expected that a thin and lightweight light source module is achieved by using side light sources, similarly to the small and medium sized liquid crystal display devices.
In conventional techniques, the light source module uses cylindrical lenses as optical systems to focus light emitted by light emitting diodes on a light guide plate having side surfaces, each of which faces upper surfaces of the light emitting diodes. The light emitting diodes are sealed by transparent cylindrical resin to achieve various line light sources such as a light source for an illumination device and a backlight source module for a liquid crystal display device.
Each of JP-A-2005-148095 (refer to paragraphs 0034, 0051-0062, FIGS. 3 and 6) and JP-A-2005-148440 (refer to FIGS. 3 and 4) discloses a technique using cylindrical lenses as an optical system for a liquid crystal display. In JP-A-2005-148095, the optical system uses an optical sheet with the cylindrical lenses to reduce irregular brightness, moiré, and mechanical damage. In JP-A-2005-148440, a light blocking pattern defined by optical factors is provided at a non-light collecting portion of a lens section to ensure that light output from a non-light blocking part (opening) is directed by the lens section towards a liquid crystal panel. The construction of the optical system exhibits viewing angle characteristics providing a bright display image to a lot of viewers.